1. Field
The present disclosure relates generally to antennas, and more specifically, to compact antennas for Ultra Wide Band applications.
2. Background
Portable devices capable of wireless communications are currently available in several different forms, including mobile telephones and personal digital assistants (PDAs). A portable device such as a wireless modem may also be used to provide such capabilities to a laptop or other computer. The technology supporting these devices is expanding rapidly and today includes such features as Internet access, email services, simultaneous transmission of voice and data, and video. Ultra-Wideband (UWB) technology is just one example of emerging technology being developed to support such devices. UWB provides high speed communications over an extremely wide bandwidth. At the same time, UWB signals are transmitted in very short pulses that consume very little power.
UWB antennas need to have an operating frequency band between 3.1 to 10.6 GHz. These antennas typically occupy a larger volume than conventional narrow band antennas. This can pose a problem in most practical applications especially when the antenna is intended for a portable wireless device where the real estate is scarce. The situation may become even worse when there is a need to use diversity combining techniques where at least two antennas need to share the available real estate.
One type of antenna commonly used in high bandwidth applications is the chip antenna. A chip antenna includes a ceramic substrate supporting metallic traces positioned over a ground plane with the ground removed from underneath the chip. One problem with this antenna is that the ground plane tends to increase the overall size of the antenna. Although, the ground plane for the printed circuit board supporting the electronics may be used in some applications, the antenna dictates the size of the plane which is not desirable. Also, induced RF currents on the printed circuit board may cause receiver desensitization, thereby limiting the useful range of the portable wireless device. In diversity applications, there would be increased coupling between the antennas since they share the same ground plane, thereby reducing diversity gain.
Accordingly, there is a need for a high bandwidth compact antenna for portable wireless devices. The high bandwidth compact antenna should be designed in a way that does not significantly degrade the performance of the electronics.